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Knowledgebase: Data processing
What are the primary data products that the SSC generates? What is a BCD? What is a post-BCD product?
Posted by z-Schuyler Van Dyk on 02 December 2008 11:45 AM
In general, the eight SSC data processing pipelines convert spacecraft engineering data into scientifically useful data. Raw data (engineering and science) are received at the ground tracking stations via telemetry and forwarded to the Spitzer Flight Operations Center at the Jet Propulsion Laboratory in Pasadena. The Flight Operations System at JPL receives telemetry packets from the Spitzer spacecraft and repackages them into FITS files containing sensor data, expressed in DN (data number) units. Instrument engineering and housekeeping data are also transferred to the SSC from the Flight Operations System. The archived raw data represent rationally organized, time-ordered data and include associated Observatory pointing data and calibration observations.

Basic Calibrated Data (BCD) are two-dimensional images in FITS format, and correspond to individual 'data collection events (DCEs)' within an observation. An image is flux and/or wavelength (if appropriate) calibrated, and surface brightness measurements are expressed in physical units. In addition, flat-fielding and cosmetic restoration (e.g., cosmic-ray removal) algorithms are applied to the BCD. Spatial 'world' coordinates are derived from Observatory pointing information only. The BCDs represent the most reliable product achievable through automated processing.

Extended pipeline products (also referred to as Post-BCD products, previously referred to as Browse Quality Data) are also available. The exact nature of these data will likely change throughout the mission, as more sophisticated analysis tools are developed by some combination of the SSC, Instrument Teams, and the Legacy Science teams. For example, higher-level imaging products include co-addition, mosaicing, and source extraction.

The description of SSC data products depends on the science instrument and observing mode. High-level descriptions of BCDs for each of the observing modes are available in the Spitzer Observer's Manual, and details appear in the corresponding Data Handbook (IRAC, IRS, MIPS).

The SSC provides routine calibrations for each of the observing modes. These data enter the Spitzer public archive immediately upon processing and verification (unless a proprietary observation embargoes the release of the data). The investigator may propose to undertake special calibrations, although the required observing time to do so must be explicitly requested in the proposal. For Legacy Science projects, these special calibration data also enter the public archive immediately upon processing and verification.